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aran
Joined: 19 Apr 2010
Posts: 70
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 Posted: Sat Jun 30, 2012 8:05 am Post subject: |
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| ronk wrote: |
Perhaps too subtle |
I'm taking it that not even you dispute the elimination rule...
In the example then, when the solver comes to consider eliminations based on candidate 4 in the ALS {347} he sees before him 4r7c6 and 4r8c1.
He is on the point of noting these eliminations, when he remembers that post of ronks
Up until then life was easy.
Now if he first saw 4r7c6, then 4r8c1 must no longer be recorded as a direct elimination, it has become a consequence
On the other hand, if he first saw 4r8c1, then 4r7c6 becomes the mere consequence.
But if he can't remember which he saw first, he must regard the one as a consequence of the other, even though he cannot say which way round (very unpleasant for the solver)
If he saw both at the same time, he must now impose an arbitrary order on his vision (yet more frustration for the solver).
By the way, for that latter circumstance, what do you generally recommend : coins or dice ? |
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Luke451
Joined: 20 Apr 2008
Posts: 310
Location: Southern Northern California
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| Posted: Sat Jun 30, 2012 3:46 pm Post subject: |
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Xsudo found this variation of the Sue de Coq, and it includes the other elimination.
The program called it "Sue de Coq, Locked."
I was unable to force the program to search for doubly-linked ALS, but I'm sure it's capable of doing so.
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aran
Joined: 19 Apr 2010
Posts: 70
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| Posted: Sun Jul 01, 2012 8:00 pm Post subject: |
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Referring to the xsudo grid put up by Luke :
5 base sets :
- 5 cells r389c3+r7c12
6 covers sets :
- 26c3+37b7+4b7+4r7
At first sight therefore a structure of rank 6-5=1.
However 4b7 and 4r7 constitute duplicate cover for 4r7c12 (either on its own being sufficient).
So rather than a rank 1 structure there are two slightly differing rank 0 structures, allowing eliminations in both duplicate cover sets ie <4>r8c1+<4>r7c6.
The human solver - under the simplicity of the DL-ALS concept - merely eliminates all candidates 4 satisfying the elimination rule (anything which would lock an ALS is false).
NB possible that the exchange with ronk may have been at cross purposes : he may have been referring all along to the rank 0 structure in the xsudo grids he posted, and not to the SDC under consideration (by me at any rate). In those grids, ALS {347} does not feature, but on the other hand cell r8c1 is a cover set for 26r8c1, leading to elimination of 4r8c1, hence establishing 4r7c12, with as consequence <4>r7c6 |
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